2002 Fiscal Year Final Research Report Summary
Theory of non-linear wave forces acting on an offshore structure in a shallow water and comparison with experiments
| Project/Area Number |
12450406
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
海洋工学
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| Research Institution | The University of Tokyo |
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Principal Investigator |
KINOSHITA Takeshi The University of Tokyo, Institute of Industrial Science, Professor, 生産技術研究所, 教授 (70107366)
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| Co-Investigator(Kenkyū-buntansha) |
SANO Ikou The University of Tokyo, Institute of Industrial Science, Research Associate, 生産技術研究所, 助手 (90238220)
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| Project Period (FY) |
2000 – 2002
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| Keywords | non-linear wave force / ringing / moored floating body / secular term / wave drift damping / wave drift added mass / wave drift force |
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| Research Abstract |
Non-linear wave forces act essential role on non-linear responses of an offshore structure such as a tension leg platform. It has not been established yet to theoretically estimate them in case of higher than 3^<rd> order. It is mainly because of secular terms which appear in a free-surface condition in case of perturbation approach. Molin shown that numerical filtering is useful to avoid them, but his method cannot apply to the problem in case of shallow water. In this research we have formulated 3^<rd> order wave force acting on a circular cylinder in shallow water, and studied general mathematical behavior of the secular terms. Another important and interesting subject of a secular terms is a wave drift added mass, which is very important to estimate slow drift oscillation of a moored floating body in irregular waves, as well as a wave drift damping. We have formulated the problem by a perturbation method with two small parameters which are wave slope and motion frequency. Secular terms appear in the higher order problems, similarly to the 3^<rd> order wave force problem. We have firstly obtained radiation conditions to set unique solutions. The obtained solutions were compared with the measured date obtained by newly developed experimental set-up.
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